Epcot is certainly a place to spend a lot of time. Of course Kidcot where they can color and get their name written in the native language as well as talk to the Cast members, it is really priceless.
My DD4 & DD& (at the time) were coloring in Japan and the CM was making little origami frogs and started flicking them at the girls and then looking away, it was so adorable, the kids laughed and laughed and started flicking them back. He showed them how to make and gave a few to take with. really, priceless, you can't plan those kind of interactions.
Also they try on hats/outfits in almost all of the countries, play with the local toys, etc. Have a treat in several. It has been a wonderful way to expose them to cultures they know nothing about.
Lastly, the entertainment in Epcot is AWESOME! Chinese acrobats, Celtic Rock band in Canada, World Showcase players doing plays in middle of street, Japanese drummers, the list goes on and on!!!
Oh yeah, plus there are some really cool things to see in the countries, Koi pond in Japan, Train village (with hidden Mickey) outside Germany....
ok, enough, sorry. We love Epcot and spend 2 full days here! As many others said, you have to know your family. We have never done a waterpark in our 4 trips because we wanted to take all the time in the other parks....